As semiconductor device geometries continue to shrink, more emphasis has to be placed on improved, interconnect structures to minimize resistance-capacitance (RC) delays. Strategies to minimize interconnect delays include improving the conductivity of the interconnect metal and lowering the dielectric constant k value of the insulating dielectric layers. For example, copper has emerged as a replacement for conventional aluminum as the interconnect metal in advanced devices down to the 20 nm or even lower node. Copper is more conductive than aluminum (thus reducing resistance-capacitance time delays) and is also less subject to electromigration when compared to conventional aluminum metallization.
In the manufacture of deep submicron semiconductor devices comprising large-scale (LSI), very-large-scale (VLSI) or ultra-large-scale (ULSI) integration, the copper damascene process is used to form conductive copper lines and vias in the low-k or ultra-low-k dielectric layer. One important step of the damascene process is the chemical mechanical polishing (CMP) of copper for the removal of excess copper above the dielectric layer surface. Customarily, barrier layers containing or consisting of tantalum, tantalum nitride, titanium nitride or ruthenium are located between the copper metal and the dielectric layer materials in order to prevent the diffusion of copper into the dielectric material.
The CMP process itself involves holding and rotating a thin, flat substrate of the semiconductor device against a wetted polishing pad under controlled pressure and temperature in the presence of CMP slurries. The CMP slurries contain abrasive materials and various chemical additives as appropriate to the specific CMP process and requirements. Following the CMP process, contaminants and residues consisting of particles from the CMP slurries, added chemicals, and reaction byproducts are left behind on the polished substrate surface. In addition, the polishing of a substrate surface having copper/low-k or ultra-low-k dielectric materials often generates carbon-rich particles that settle onto the surface after CMP.
However, all residues and contaminants must be removed prior to any further steps in the microelectronic device fabrication process to avoid degradation of the device reliability and introduction of defects into the microelectronic devices.
Various alkaline and acidic chemistries have been proposed in the past for the removal of such residues and contaminants from the surface of the polished semiconductor substrates.
Thus, the international patent application WO 2006/127885 A1 or the American application US 2008/0076688 A1 both disclose an aqueous alkaline cleaning composition for post-CMP cleaning comprising at least one amine, at least one passivating agent such as benzotriazole (BTA), optionally at least one quaternary ammonium hydroxide such as TMAH and optionally at least one reducing agent. It is believed that the passivating agent forms a layer consisting of a passivating-copper complex on top of the copper/copper (I) oxide surface such that solid particles can be easily removed by the cleaning composition. This strategy is also termed “displacement cleaning”.
The American patent application US 2009/0239777 A1 discloses an aqueous alkaline post-CMP cleaning composition comprising at least one corrosion inhibitor and at least one amine wherein the corrosion inhibitor is selected from the group inter alia consisting of glucuronic acid, squaric acid, ascorbic acid, flavonols, and anthocyanins. The composition may contain reducing agents such as gallic acid, polyols such as diols and triols, amphiphilic nonionic surfactants such as polyethylene glycols, polypropylene glycols, polyethylene or polypropylene glycol ethers or dinonylphenyl polyoxyethylene, dispersing agents such as acrylic acid-containing polymers, and complexing agents such as formic acid, acetic acid, propionic acid, acetone, 2,4-pentanedione, acrylic acid, adipic acid, fumaric acid acid, gluconic acid, glucuronic acid, glyoxylic acid, maleic acid, malic acid, malonic acid, mandelic acid, phenylacetic acid, phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, succinic acid, pyrocatechol, trimellitic acid, trimesic acid, tartaric acid, citric acid, sorbitol and xylitol.
The alkaline amine-containing post-CMP cleaning compositions exhibit various disadvantages. Thus, smell and release amine vapors into the fab which can poison the photoresists.
Therefore, aqueous, acidic post-CMP cleaning compositions have been developed, as for example, the composition disclosed in the American patent application US 2010/0286014 A1 which comprises at least one surfactant, at least one dispersing agent, and at least one sulfonic acid-containing hydrocarbon. Suitable surfactants are amphiphilic nonionic surfactants such as polyethylene glycols, polypropylene glycols, polyethylene or polypropylene glycol ethers or dinonylphenyl polyoxyethylene. Suitable dispersing agents are acrylic acid-containing polymers. Optionally, complexing agents such as formic acid, acetic acid, propionic acid, acetone, 2,4-pentanedione, acrylic acid, adipic acid, fumaric acid and itaconic acid, gluconic acid, glucuronic acid, glyoxylic acid, maleic acid, malic acid, malonic acid, mandelic acid, phenylacetic acid, phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, succinic acid, pyrocatechol, pyrogallol, trimellitic acid, trimesic acid, tartaric acid, citric acid, sorbitol and xylitol can be used.
Moreover, the American patent application US2009/291873 A1 discloses an aqueous post-CMP cleaning composition having a pH in the range of from 2 to 11 obligatorily comprising a compound containing an amino acid group and/or a betain group. The composition optionally contains a pH modifier chosen from an organic acid and/or an organic base, a surfactant and a chelating agent. Amphiphilic nonionic surfactants such as polyalkylene oxide surfactants can also be used. Suitable amphiphilc nonionic surfactants include octyl and nonyl phenol ethoxylates such as Triton™ X-114, X-102, X-45 and X-15 and ethoxylated alcohols such as BRIJ™ 56 (C16H33(OCH2CH2)100OH or BRIJ™ 58 (C16H33(OCH2CH2)20OH), alkyloxylated acetylenic diol surfactants, glucosides, polyethylene glycols and polyethylene-polypropylene glycols. Additionally, corrosion inhibitors may also be added. Suitable corrosion inhibitors are anthranilic acid, gallic acid, benzoic acid, isophthalic acid, fumaric acid, phthalic acid, maleic anhydride, phthalic anhydride, fructose, lactic acid, dihydroxy benzene and trihydroxy benzene.
However, both, the alkaline and the acidic post-CMP cleaning compositions have their drawbacks. Thus, they increase the surface roughness of the polished copper surfaces due to redox reactions which cause etching, corrosion and pitting. The etching components of the compositions can chemically undercut the particles on top of the polished surfaces thus creating additional defects such as voids. The surfactants used in the prior art compositions are frequently not able to remove the abrasive particles efficiently. This necessitates strong etchants for undercutting the abrasive particles. However, such strong etchants can increase corrosion. The presence of barrier metals such as tantalum, tantalum nitride, titanium nitride or ruthenium can lead to an increased galvanic corrosion. Therefore, the strong acidic or alkaline process conditions require strong copper inhibitors such as BTA in order to avoid copper damage by high local or global static etch rates. However, strong copper inhibitors such as BTA are water-insoluble hydrophobic compounds and, therefore, are easily absorbed by the polished copper surfaces to form a passivation film which requires solvents such as amines for its removal. Last but not least, the cleaning compositions are capable of attacking the low-k and ultra-low-k dielectric materials surrounding the copper wirings and vias.